If you do not enable DKIM, Office 365 automatically creates a 1024-bit DKIM public key for your custom domain and the associated private key which we store internally in our datacenter. By default, Office 365 uses a default signing configuration for domains that do not have a policy in place. This means that if you do not set up DKIM yourself, Office 365 will use its default policy and keys it creates in order to enable DKIM for your domain.

For DKIM, you need 2 records - i use godaddy for dns and used these values:
CNAME is selector1._domainkey
Points to selector1-mydomain-net._domainkey.mytenant.onmicrosoft.com

Create a second set using selector2 instead of selector1.

If the value isn't correct, when you try to enable it, office 365 will give you the correct value to use.

I got this back from powershell (the web interface method will also show it, but its harder to copy)

Code:

PS D:\Documents\WindowsPowerShell> New-DkimSigningConfig -DomainName outlook-tips.net -Enabled $true
WARNING: The config was created but can't be enabled because the CNAME records aren't published. Publish the following
two CNAME records, and then enable the config by using Set-DkimSigningConfig.
selector1-outlooktips-net01i._domainkey.Cdolive.onmicrosoft.com
selector2-outlooktips-net01i._domainkey.Cdolive.onmicrosoft.com

DMARC is one text record:
_dmarc
v=DMARC1; p=quarantine

The recommendadtion is to use p=none to test, but if you aren't using 3rd party mailing services, quarantine is probably ok.

The raw header has the following- i also sent one to an outlook.com account, it is the same but with outlook.com instead of google menyioned in the header. Outlook.com adds a best guess on dmarc though: dmarc=bestguesspass action=none header.from=poremsky.com;

Who hosts your DNS records? I'm assuming if Microsoft does, that they set this up, but i don't use them so i cant say for sure. (And i don't think you can edit the DNS records if they are the nameserver) (if the domain in the header above is correct, Microsoft is the nameserver.)

Go to Sign in to your account - click Admin center at the bottom, choose Exchange. Find DKIM link (its under protection) - select the domain and click Enable on the right.

I'm not exactly sure where you'll see the name servers at Sign in to your account - but go there and look around. Maybe select the domain, then click Check DNS - that is where i se this for my domains:Add the DNS records for me (recommended)
Since GoDaddy is your DNS hosting provider, all you have to do is sign in and we'll update your DNS records.

I'm not exactly sure where you'll see the name servers at Sign in to your account - but go there and look around. Maybe select the domain, then click Check DNS - that is where i se this for my domains:Add the DNS records for me (recommended)
Since GoDaddy is your DNS hosting provider, all you have to do is sign in and we'll update your DNS records.